Vacuum suction moulding is generally used to make open shell products of thermoplastic sheets. The principle is simply to heat the plastic sheets to a certain temperature, soften them to viscoelastic state, and then vacuum the mold through vacuum pump suction. The pressure difference forms vacuum suction, so that the sheets are covered on the contour surface of the mold after deformation. After cooling and shaping.
The whole vacuum suction unit is generally composed of upper and lower heaters, temperature controllers, bearing plates, pressing frames, vacuum pumps, vacuum chambers, mould temperature controllers, cooling devices, etc. The parameters are controlled by computer storage, and the control is simple. When a certain type of product is produced, only the corresponding parameters can be adjusted.
Vacuum suction molding relies on vacuum pressure difference to make sheet tensile deformation. At present, the vacuum is easy to realize, master and control, which makes the vacuum suction molding products have the advantages of low price and high production efficiency, and has been widely used. It can be divided into three forms: die-less forming, punch (positive) forming and concave (negative) forming.
Vacuum mouldless forming is that the sheet is heated to the required temperature, pressed on the clamping ring, and then vacuum pumped. By controlling the vacuum degree, the sheet reaches the required forming depth. In this method, the parts do not touch any die surface, the surface gloss of the parts is high, and there are no defects. However, during the forming process, the drawing degree and the outline shape of the parts can only be changed, and the parts with complex shape can not be formed.
The difference between punch (positive) forming and concave (negative) forming is that the contact surface between the forming material and the forming die is different. The products formed by them are of high quality on one side of the cavity wall, and the structure is more distinct and meticulous. However, the punch forming is more advantageous for the manufacture of products with larger wall thickness and depth, while the die is not suitable for the production of products with large depth. At the same time, they have their own characteristics in dimension accuracy and product thickness. The inner dimension of the product is accurate, the largest part of the wall thickness is at the top of the punch, the thinnest part is at the junction between the side and the bottom of the punch, the outer dimension of the product is accurate, the largest part of the wall thickness is at the bottom of the cavity, the thinnest part is at the junction between the side and the bottom of the cavity, and with the increase of the depth of the cavity, The wall at the bottom corner of the product becomes thinner.
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